In conventional air-conditioning apparatuses such as a multi-air-conditioning apparatus for a building, cooling operation or heating operation is carried out by circulating a refrigerant between an outdoor unit that is a heat source device disposed outdoors and indoor units disposed indoors. Specifically, a conditioned space is heated with the air that has been heated by the refrigerant transferring heat to the air and is cooled with the air that has been cooled by the refrigerant removing its heat. Regarding the refrigerant used for such an air-conditioning apparatus, hydrofluorocarbon (HFC) based refrigerant, for example, is typically used. An air-conditioning apparatus using a natural refrigerant, such as carbon dioxide (CO2), has also been proposed.
There is also an air-conditioning apparatus having a different configuration represented by a chiller system. Further, in such an air-conditioning apparatus, cooling or heating is carried out such that cooling energy or heating energy is generated in a heat source device disposed outdoors; a heat medium such as water or brine is heated or cooled in a heat exchanger disposed in an outdoor unit; and the heat medium is conveyed to indoor units, such as a fan coil unit, a panel heater, or the like, disposed in the conditioned space (for example, see Patent Literature 1).
Moreover, there is an air-conditioning apparatus called a heat recovery chiller that connects a heat source unit to each indoor unit with four water pipings arranged therebetween, supplies cooled and heated water or the like simultaneously, and allows the cooling and heating in the indoor units to be selected freely (for example. see Patent Literature 2).
In addition, there is an air-conditioning apparatus that disposes a heat exchanger for a primary refrigerant and for a secondary refrigerant near each indoor unit in which the secondary refrigerant is conveyed to the indoor unit (see Patent Literature 3, for example).
Furthermore, there is an air-conditioning apparatus that connects an outdoor unit to each branch unit including a heat exchanger with two pipings in which a secondary refrigerant is carried to the corresponding indoor unit (see Patent Literature 4, for example).